In the past, various ways have been utilized for changing the pile height of the tufts of the tufting machine. Usually to change the stroke of the needle bar is quite time consuming and entails a shut down of the machine.
Another way of changing the pile height of the tufts sewn into the backing material is through the control of the yarn feed of the tufting machine so as to rob yarn from the previously sewn loop as the needles descends through the backing material.
Still other methods of controlling the pile height of tufts formed in a backing material has been to provide screw jacks which can be manipulated to raise and lower the bedrail. U.S. Pat. No. 3,881,432 granted to Dodd, et al., discloses such an adjustable bedrail supported by a plurality of screw jacks which are simultaneously rotated manually or by power. Such a procedure is quite imprecise and time consuming.
In the prior art, the hydraulic clamps or brakes have been manually operated. In doing so, the operator would look at a dial indicator which was mounted above the bedrail. The operator would then turn a rack and gear setup handwheel such that the bedrail would be raised and lowered. The serious disadvantage with that prior art system independently was that the loading and unloading of that system would account for 0.010 to 0.050 inch of error. So for the operator to get to an accurate position for the bedrail, he would actually have to lower the bedrail about a 0.1 inch below where he needs to go and then change direction and go back up to the location that he needs. In changing the bedrail position in a cut pile operation of the prior art machine, what the operator would have to do is very time consuming in that he would actually have to jog the machine to get the loops off the loopers. He would then have to raise the bedrail a small amount, whether it be a 0.1 inch or 0.2 inch--whatever he could physically pull the bedrail up to, before he felt the yarn tension was too tight. At that point he would then increase the yarn feed rate, whether that meant changing V-belt ratios on the end of the machine or by changing the amount yarn feed, whichever system, he would have to effect an increase in yarn feed. He would then have to stop the process again and manually unclamp the brakes and raise the bedrail again. So, for a 1/2 inch height change, he might have a 15 minute operation. His margin of error in the prior art method was very imprecise because his dial indicator is most often just a measure of how far he's moved relative to this one time. So, there has never been an absolute position on the bedrail in the past. In other words, using the prior art system, if the pile height needed increasing about 0.2 inch, the operator would know he needs to move the bedrail about 0.2 inch up. There would be no actual set position for the bedrail so that he could return to the same setting, in the future. If an operator wanted to come back and run this exact set up a month later, he would not have an accurate way of doing this.
In the prior art, clamp hydraulic cylinders 46 were controlled by a mechanical pump and the operator actually turned a handwheel which actually operated the pump. In other words, the operator would actually pump the pressure into the hydraulic system by hand.
U.S. Pat. No. 4,867,080 granted to Brooks E. Taylor, et al. discloses a computer controlled tufting machine providing a bedrail height adjustment which utilizes a stepping motor for raising and lowering the bedrail. This stepping motor, in turn, is controlled by the computer. This form of structure will enable the remote controlling of the motor which actuates the screw jacks to raise and lower the bedrail. Problems, however, exist in making certain that the bedrail is disposed at a precise height in the tufting machine as dictated by the computer. The screw jacks, for example, sometimes become rusted and worn so as to locate the bedrail at only the approximate desired location and the stepping motor may rotate after being shut down, due to the vibrations.